This invention relates to liquid cooled thyristor columns having disk thyristors which are elastically held between heat sinks and in which the heat sinks are also used as conductors for electrical current conduction in general and more particularly to an improved method of cooling such a thyristor column which permits cooling the thyristors with unpurified liquids such as water.
Thyristor columns in which a plurality of disk thyristors, each elastically held between heat sinks on each side are arranged in a column are described, for example, in German Offenlegungsschrift No. 1,914,790.
Such thyristor columns are used in bridge circuits wherein a plurality of disk thyristors must be connected in series. For providing liquid cooling in such thyristor columns the heat sinks are installed in a coolant circulation system through insulating intermediate sections. Unpurified coolants may be used, i.e., coolants of low electrical conductivity such as the cheapest coolant water, only if a low voltage is applied to the disk thyristors and if connection paths between the heat sink are suitably long. If higher voltages, e.g. 3kV, are present at the disk thyristors, either the connection paths between heat sinks must be made so long as to not be economically acceptable and/or technically feasible or de-ionized water or another electrically non-conductive liquid must be used as the coolant.
There are known from German Offenlegungsshrifts 2,107,008, 2,107,009, and 2,107,319 various means for cooling disk thyristors using air. In the disclosed arrangements a heat pipe is placed on each of the two end faces of the disk thyristor. Each unit comprising a disk thyristor and two heat pipes is clamped using a clamping device. Cooling fins are provided on the free ends of the heat pipes to enlarge the heat transfer surfaces for a gaseous cooling medium. What is referred to as a heat pipe will be understood by those skilled in the art as that which is described in U.S. Pat. No. 2,350,348 or in the journal "Chemie-Ingenieur-Technik", volume 39, 1967, No. 1, pages 21 to 26. Briefly, a heat pipe comprises a tube or pipe closed on both ends and having its inner wall covered with a wick of capillary structure. The wick is saturated with a liquid working or operating fluid such as freon, methanol, ethanol, acetone, benzene or water. When the portion of the heat pipe termed the vaporization section is heated, the operating liquid vaporizes from the wick and the vapor flows in the direction of lower temperature. At the other end, which is cooled and termed the condensation section, the vapor gives off its heat of vaporization and is again liquefied. The liquid operating fluid is then transported back to the vaporization section of the heat pipe by means of capillary action. In such a heat pipe circulation is obtained for the operating fluid which circulation is independent of position, i.e., it is independent of external forces and can also operate against the force of gravity.
In German Utility Model No. 7,224,356 or German Offenlegungsshrift No. 2,120,474 an electrically insulated heat pipe is described. In that heat pipe the vaporization and condensation sections are electrically insulated from each other by means of a tubular intermediate section of insulating material. Naturally, in such a heat pipe the wick, at least in the zone of the intermediate section of insulating material, and the operating fluid must be electrically non-conducting.
In U.S. Patent application Ser. No. 491,779 now U.S. Pat. No. 3,942,586 an air-cooled thyristor column having disk thyristors is proposed in which devices such as those known from German Offenlegungsshrift Nos. 2,204,589 or 2,107,008 are stacked so that the axes of the heat pipes of superposed heat sinks are rotationally offset relative to each other and with respect to the stackaxis. In this gas cooled thyristor column excellent cooling of all heat pipes is obtained.
It can be seen from the above, that, although liquids are better cooling mediums than gases, problems arise when attempting to liquid cool at high voltages. Thus, it can be seen that there is a need for a liquid cooled system in which an unpurified liquid coolant such as water can be used with such high voltage installations.